Generally oscillators are known. A general model for transistor based oscillators has been described. This model includes a three terminal transistor with a generalized impedance connected between each terminal. This model purports to describe all popular oscillator configurations when one at a time each terminal of the transistor is individually grounded. That and numerous texts concerning the topic notwithstanding, practitioners continue to devote an extensive amount of effort to improving and creating oscillators that serve their particular purposes.
The operative word for all such efforts is compromise. The practitioner is continually asked to make tradeoffs between oscillator power, power consumption, noise performance, frequency stability, tuning range, interference susceptibility, physical space, and economic considerations. Most such efforts now utilize some form of transistor based active circuit. Transistors contribute their own set of problems for the oscillator practitioner due to there inherent non-linearities, noise properties, and temperature variations.
One oscillator presently used is a transistor based common collector configuration known as a Colpitts oscillator. This arrangement often includes from an alternating current (ac) perspective a resonator or simple inductor and parallel coupled thereto a circuit including an npn transistor with the base coupled to the resonator or inductor, a base emitter connected capacitor, and a capacitor series connected from the emitter to the resonator or inductor. Texts and practitioners counsel operation of the transistor with a relatively low magnitude reactance or large value capacitor across the base emitter in an attempt to overcome temperature variations and non-linearities of the transistor.
Unfortunately, at UHF of higher frequency, when the inductor is replaced with a high impedance resonator, this results in a relatively lower loaded Q factor (Q) and thus lower signal to sideband noise ratio for the oscillator which is a particular disadvantage for oscillators used as a reference source or as a voltage tuned oscillator. To compensate, the unloaded Q for the resonator or inductor must be increased at a net and often substantial increase in the size or cost of that component and the resultant oscillator circuit. Clearly a need exists for a small relatively high performance oscillator that may be advantageously employed as a voltage variable oscillator